Microsampling

Advances in bioanalytical techniques have opened up the potential to use smaller sample volumes (microsamples) to assess drug and chemical exposure in blood, plasma and/or serum. It is now possible to assess drug levels and blood biochemistry parameters from samples of 5-20µl.

A microsample generally refers to a sample of ≤50µl. The small sample volume required enables samples to be taken from the main study animals which reduces or avoids the use of satellite animals. The sampling procedure provides a refinement because microsampling is quicker and less stressful, for example, warming of animals can be reduced or avoided.

Microsampling is used by many companies in early studies, such as those in discovery and for dose range finding. However there are scientific, business and animal welfare incentives to implement microsampling more widely within other toxicology and nonclinical studies where blood sampling is performed. Uptake for GLP toxicology studies was slower due to perceived regulatory hurdles and concerns that sampling from main study animals will compromise key endpoints. Many of these concerns have been addressed [1-4] and microsampling is now also routinely included in many regulatory studies.  Additionally, updates to international regulatory guidance in 2017 [5] support and promote microsampling.

The aim of this web resource is to guide strategy and encourage adoption of microsampling techniques within academia and the pharmaceutical and chemical industries.

There are multiple advantages associated with microsampling including scientific, resource related and animal welfare benefits, which are summarised in the diagram above. Many aspects overlap (e.g., needing fewer animals leads to resource benefits of reduced housing and technician time). 

Scientific benefits

• Ability to relate toxicity directly to exposure in the same animal.
• All animals are sampled in the same way.
• Multiple endpoints can be assessed in one animal.
• More timepoints within toxicokinetic profiles.

Animal welfare benefits

• Blood loss from the animal is reduced. This is particularly important when multiple samples will be taken and for species with less total blood, such as mice and rats.
• The procedure is less invasive. Smaller needle gauges are required and capillary action pin pricks avoid full needle insertions.
• Alternative, refined sampling routes can be used. Taking smaller blood volume means that less invasive sampling routes are possible. For example, terminal routes can be avoided or the pig ear vein can be used instead of the jugular vein.
• Reduced restraint time and/or alternative, refined restraint methods can be used. For example, rats can be restrained in the crook of the arm; restraint can be refined when sampling from the pig ear vein compared to the jugular vein.
• Reduces the need for pre-vasodilation. Warming time is reduced (e.g. for mice and rats) and topical vasodilation solutions are not required (e.g. for rabbits).
• The reduced overall procedure time is less stressful for the animal. A combination of the above factors improves the efficiency of the blood sampling procedure and refines the overall process. 
• To learn more about how microsampling improves animal welfare compared to traditional blood sampling methods watch the recorded talk on Animal welfare benefits of microsampling for any purpose from Dr Hollie Blunt at Sequani.

Resource benefits

• Less test material is required.
• No satellite animals or smaller satellite groups means fewer animals are required.
• Fewer animal-related resources, such as housing and care, is required.

Microsampling is applicable for any species; the advantages such as quicker sampling time and less-invasive procedure are refinements of equal benefit to non-rodents, where blood volume considerations are generally not as critical as for rodents. 

There are many considerations that need to be taken into account to implement microsampling within your organisation and for a specific compound. Some of these considerations may have been covered in our 2022 webinar Microsampling in toxicology – Maximising the scientific, business and 3Rs advantages.

This decision tree below can help to determine if your study is amenable to microsampling, and which is the most relevant approach (for example microsampling from a group of satellite animals or from main study animals).

For more information on sampling techniques in general, refer to our blood sampling pages.

Microsampling can reduce or avoid the use of satellite groups, reducing the overall number of animals required for a study. We have created examples of study designs that may be used for microsampling from either main study animals or from satellite groups of animals. This guidance is intended to be a starting point for study design.

In September 2022, in collaboration with the British Toxicology Society (BTS), we hosted the webinar Microsampling in toxicology – Maximising the scientific, business and 3Rs advantages to raise awareness of the microsampling technique and encourage wider adoption across both discovery and regulatory toxicology studies. Visit the microsampling webinar session recordings page to watch the presentation recordings.

Rat microsampling (Vivonics)

Drummond™ capillary method

A closed system collection using the Drummond™ Aqua-Cap®

Blood collection using Microvette® tube

Using the Mitra™ sampling device

To further increase uptake of microsampling, we lead an international microsampling user group which includes 27 companies and regulators. We act as an honest broker for data sharing - the evidence that we collated fed into the updates to regulatory guidelines [5] and is published within peer-reviewed journals [6-8]. 

We initiated an industry survey to establish how widely microsampling was used within the pharmaceutical and agrochemical industries. Data was collected between December 2020 and April 2021. Work is ongoing to address the current barriers identified.

Some of the results of the survey were presented at a talk by Dr Helen Prior, NC3Rs as part of our 2022 microsampling webinar.